The World Trade Center disaster in New York City on Sep. 11, 2001 has highlighted the need for an apparatus to provide for the rapid and safe evacuation of large numbers of persons along the exterior of a high-rise building during a major fire or other life-threatening emergency when the stairwells are inaccessible, unusable, overcrowded, smoke-filled, obstructed, or otherwise unsafe.
Major fires in high rise office buildings and hotels often trap people on the floors above, stranding them to succumb to smoke inhalation, carbon monoxide, and fire, or to leap to their deaths (as nearly 200 did during the WTC disaster). Thus there exists the need for an apparatus capable of getting large numbers of people very quickly out of the deadly interior of a burning building into the fresh air on the smoke-free side of the building, then lowering them to the ground (or other safe surface below the fire), very slowly so they can maneuver safely past hazards presented by the facade of the building and each other, and land on the ground (or the other safe surface) injury-free, regardless of the building's height or shape. Even with the fastest possible escape to the outside, some of the people will have to brave the deadly gases inside for at least a while, so the apparatus should also include a means for providing them breathable air during that time.
The host of devices available or proposed for escaping from high-rise buildings include low-altitude parachutes, tubular net life-chutes, aerial vertical takeoff and landing (VTOL) rescue platforms, and controlled descent devices. The low altitude parachutes cannot be used below the 15th floor, and they can collapse if the novice parachutist drifts into the side of his or an adjacent building, something even an experienced parachutist is likely to do. Tubular net life chutes are limited, both in their numbers and locations in a building, thereby significantly limiting the number of people they can save. And they can blow uncontrollably in high winds, making them impractical to use on very tall buildings. VTOL rescue platforms are only in the proposal stage, with the largest claiming to hold only up to ten people. Controlled-descent devices may be user-controlled, or automatic. With the user-controlled type, the person controls his speed by continually adjusting the friction applied to a rope that's suspended from the departure point down to the ground. However, it requires training and skill and isn't practical from great heights. Although the automatic type can be used by untrained persons, it is heavier and more expensive. Thus it is typically employed up at the departure point to mete out the rope or cable—usually too fast for a safe descent alongside the facade of a building, and yet too slow to evacuate hundreds of people, since each controller lets down just “one-person-at-a-time.”
To achieve the slowest descent speed and the fastest mass evacuation rate, each person needs his own wearable, light-weight, low-speed, automatic controller and cable.